1. Field of the Invention
The present invention relates to a laser device having an array structure with a plurality of luminous points, and a laser display device and a laser irradiation device using the laser device.
2. Description of the Related Art
A laser diode has features that emitted light is superior in monochromaticity, and the laser diode has a compact size and lightweight in comparison with other light sources. Thus, the laser diode is suitably utilized as a light source of a projection display or the like. However, when laser light is irradiated to an irradiated plane, a speckle pattern called speckle noise appears and a screen flickers. This is a special phenomenon caused by that the laser light has a single-wavelength and phases are aligned so that coherence is remarkably high.
To reduce such speckle noise, there are methods using an external optical element, such as a method where the laser diode is driven with high-frequency waves, a method where a diffusion plate or a diffusion sheet is vibrated, and a method where the laser light once passes through fibers having different lengths to reduce the coherence. Moreover, to reduce speckle noise, there is another method where an oscillation wavelength width of a semiconductor laser array is widened to several nm by using a phenomenon that, when the laser diode emits light, heat is generated inside the laser diode and the oscillation wavelength changes (Japanese Unexamined Patent Publication Nos. 2007-214300 and 2008-4743). Among them, the method of widening the wavelength width of the semiconductor laser array is advantageous since increasing a number of members and large-scale drive circuits are unnecessary so that reduction of speckle noise with inexpensive device configuration is possible.
In this type of laser diode, for light having a green wavelength region of the primary colors red (R), blue (B), and green (G), material system which directly oscillates with practical efficiency and reliability has been undeveloped at this point. Thus, to obtain light having the green wavelength region, there is considered a following method using wavelength conversion.
In the method using the wavelength conversion, light in an infrared region (wavelength of 1060 nm) from laser is output as fundamental waves, and the fundamental waves enter into a nonlinear optical element formed with lithium niobate (LiNb03) or lithium tantalite (LiTa03). The fundamental waves are wavelength-converted to second harmonics by the nonlinear optical element, and become green laser light with a wavelength of 530 nm. As a light source, a laser diode or a diode pumped solid state laser (DPSSL) is used.